1. Field of the Invention
The present invention relates to a semiconductor laser diode (LD).
2. Related Background Art
A multi-quantum well (MQW) structure has been widely used in an active layer of a semiconductor laser diode (LD), a semiconductor optical modulator, and the like. A U.S. Pat. No. 6,978,055B has disclosed an MQW structure with intermediate layers between well layers and barrier layers. One type of an LD implements an optical grating below the active layer having the MQW structure. When the well layers and the barrier layers show a large lattice mismatching, the epitaxial growth of those layers becomes unable to compensate discontinuity of the optical grating, which may result in abnormal growth at edges of respective corrugations of the grating.